Hierarchical Porous Carbon Monoliths Research Articles

A comparative study of nitrogen-doped hierarchical porous carbon monoliths as electrodes for supercapacitors

A comparative study of nitrogen-doped hierarchical porous carbon monoliths as electrodes for supercapacitors

A comparative study of nitrogen-doped hierarchical porous carbon monoliths as electrodes for supercapacitors

Two nitrogen-doped carbon monoliths with hierarchical porosity over a large size range were prepared by polymerization of resorcinol and formaldehyde in the presence of an organic amine, L-lysine, and an inorganic base, ammonium hydroxide under ambient conditions. Their physical and chemical features were characterized by N 2 sorption, transmission and scanning electron microscopy, and elemental analysis. Their electrochemical properties as the electrodes of supercapacitors were evaluated under both a three-electrode system and a two-electrode system. Results show that the two types of nitrogen-doped carbon possess similar pore structures, but have distinct electrochemical performances. The L-lysine incorporated carbon monolith has a high nitrogen content, a high specific capacitance of 199 F·g −1, and a 1.6% loss in the specific capacitance after 1000 charge-discharge cycles, indicating a long-term cycling stability.

Fabrication of Complex-Shaped SiC Parts Based on Polymerization -Induced Phase Separation and Pyrolysis Technique

A route based on a technique of polymerization - induced phase separation and pyrolysis (PIPSP) has been developed to fabricate complex-shaped SiC parts. The capability of this process to produce complex component shapes has been demonstrated, and corresponding reactive mechanisms have been also discussed. Three types of porous carbon preforms, i.e. mesoporous carbon monoliths (MCMs), hierarchical porous carbon monoliths (HCMs) and porous carbon foam (PCFs) were obtained, which has different pore size distributions. The pore structures of the preforms can be controlled through changing starting mixture composition and polymerizing conditions. The apparent porosity of the preform was changed from 19.9 to 60%, which was a key parameter to obtain dense SiC parts. After reactive infiltration of the preform with Si, the SiC parts were obtained. Geometry of SiC parts were controlled by molds. The dimension shrinkage of SiC parts was less than 3% before/after siliconization and no distortion occurred. Compared with other molds assistance route, the wax mold assistance route was a most potential technique to fabricate SiC parts industrially because of its suitable forming precision, recycled mold materials and low-cost. The mechanism of the reactive infiltration of MCMs was different from that of the reactive infiltration of preforms with bigger pore size, i.e. the pore channels of MCMs were restructured at transitional stage of reaction.

Resorcinol-Based Deep Eutectic Solvents as Both Carbonaceous Precursors and Templating Agents in the Synthesis of Hierarchical Porous Carbon Monoliths

Deep eutectic solvents are a new class of ionic liquids obtained via the complexion of quaternary ammonium salts with hydrogen-bond donors (such as acids, amines, and alcohols, among others). The charge delocalization that occurs through hydrogen bonding between the halide anion with the hydrogen-donor moiety is responsible for the decrease in the freezing point of the mixture, relative to the melting points of the individual components. We have recently reported on the use of deep eutectic solvents as suitable solvents, to carry out the polycondensation of resorcinol−formaldehyde. [Chem. Mater. 2010, 22, 2711−2719.] Herein, we describe the synthesis of deep eutectic solvents (DESs) based on resorcinol, the use of which as both carbonaceous precursors and structure-directing agents allowed the preparation of hierarchical porous (bimodal, with micropores and mesopores) carbon monoliths via formaldehyde polycondensation and subsequent carbonization. The performance of resorcinol-based DESs as carbonaceous precursors was remarkable, with carbon conversions of ∼80%. Moreover, the use of DESs as structure-directing agents resulted in the achievement of hierarchical porous carbon monoliths with pore surface areas up to 600 m2/g and narrow mesopore diameter distributions. The mechanism governing the formation of mesopores was based on a spinodal-decomposition-like-process via resorcinol polycondensation and subsequent segregation of the resorcinol counterpart that is forming the DESs. Thus, the use of resorcinol-based DESs that have different counterparts (e.g., either choline chloride or a mixture of choline chloride and urea) allowed the preparation of hierarchical carbons with tailored mesopore diameters of ca. 23 nm and ca. 10 nm.

Block-Copolymer assisted synthesis of hierarchical carbon monoliths suitable as supercapacitor electrodes

Three dimensional (3D) hierarchical porous (micro-, meso- and macro-porous) carbon monoliths (HCMs) have recently been proposed as promising supercapacitor electrodes. In this work, we have further explored the use of block-copolymers as templates for the preparation of HCMs via condensation of resorcinol and formaldehyde (RF) and subsequent carbonization. The resulting HCMs exhibited a textured morphology consisting of a bicontinuous macroporous carbon network built of interconnected microporous carbon colloids, as demonstrated by nitrogen adsorption/desorption isotherms, mercury porosimetry and electron microscopy, in both scanning and transmission mode. Such a texture favored the performance of HCMs as supercapacitor electrodes, reaching remarkable values of capacitance of up to 198 F g−1 (normalized by mass) and 34.5 μF cm−2 (normalized by BET surface area). The first electrolyte infiltration into the micropore (prior capacitance measurements) was demonstrated to play a crucial role in the achievement of large capacitance values.

Preparation of a carbon monolith with hierarchical porous structure by ultrasonic irradiation followed by carbonization, physical and chemical activation

A two-step direct and simple method for the preparation of a hierarchical porous carbon monolith with micropores, mesopores and macropores is described. The two stages give more flexibility in the preparation of a porous carbon monolith. In step I a macroporous interconnected carbon monolith is prepared by ultrasonic irradiation during sol–gel polycondensation. The effects of sol–gel temperature, catalyst concentration and ultrasonic power on the structure of the monolith are investigated. In step II, mesopores are induced in the monolith by Ca(NO 3) 2 impregnation followed by CO 2 activation. The effect of activation temperature is also studied. A hierarchical interconnected carbon monolith with mean pore size diameter of 1.2 μm, BET surface area of 624 m 2/g, mesopore volume of 0.38 cm 3/g and micropore volume of 0.22 cm 3/g has been obtained from Ca(NO 3) 2 impregnation of the macroporous carbon monolith followed by CO 2 activation at 850 °C.